I can see what you mean. Jaksta only detects the audio stream and so is only able to download an audio part (the video is missing).

Unfortunately it looks like we are not able to consistently capture from this site at the moment, probably depending on which server the video streams from. We may be able to add support in a future update. If you have Jaksta Screen Recorder you could try using that instead. Sorry I'm not able to be of more help here.